where is the blender rock generator addon?
You can download the add-on from here: use the "Download > Direct Download" button that will create a .zip file.

You will be able to install the add-on from File > User Preferences > Add-ons, using "Install from File" and selecting the zip file. You don't have to unzip it!

I haven't extensively tested it, but the basic features seem to work on Blender 2.79b on Ubuntu (even if the file is much older).

More in this answer by Thom Blair III. I don't know who maintains the Dropbox link above.